1. Field of the Invention
The invention is directed to a measuring device, particularly for measuring dust in the flue gas of small-scale furnace installations for solid fuels, having a measuring probe and a heated suction hose connecting the measuring probe to a weighing device with a filter device.
2. Related Art
In 2010, the First Ordinance Concerning the Implementation of the Federal Emissions Control Act was amended by the Ordinance Governing Small-scale and Medium-scale Furnace Installations (1st BImSchV) with the goal of substantially contributing to reducing emissions of fine particulates from small-scale furnace installations. In particular, the use of wood in furnace installations within the scope of the Ordinance Governing Small-scale and Medium-scale Furnace Installations can make an important contribution to achieving climate protection goals. However, the combustion of biomass can lead to emissions that are hazardous to health as well as fine particulate matter, for example, due to the release of various air pollutants.
To achieve climate goals, 1st BImSchV stipulates regular monitoring of furnace installations and prescribes maximum levels for fine particulate matter in the flue gas depending on the type of furnace installations.
For newer furnace installations, limiting values of 0.02 g/m3 are called for as of 2015. These limiting values present a challenge to metrology even though the basic principle is simple and remains the same, namely, to guide a predefined amount of the flue gas of a furnace installation through a filter and ascertain the difference of mass before and after the measuring process in order to determine the fine particulates content in the flue gas.
In order to measure such small quantities of dust, optical systems such as those described, for example, in DE 10 2006 039670 A1, DE 10 2005 009582 A1 or DE 6 9627922 T2 are currently favored in technical development.
In optical systems for determining a quantity of dust in a flue gas, the varying constitution of the dust particles and, therefore, the reflectivity thereof, must be considered fundamentally disadvantageous so that, in particular, the measurement of very small quantities of dust by optical methods seems inherently problematic.
DE 2 553 638 C2 shows an alternative to conventional scales. A device mentioned in this reference has an elastic element in the form of a hollow pipe that narrows in diameter from a clamped-in first end toward a second, free end. The free end of the pipe is widened and carries a platform-like base for articles to be weighed. The mass of the article to be weighed can be deduced from the change in the resonant frequency of the vibratory pipe in a loaded condition and when loaded by the article to be weighed. An accurate weighing of a sample appears possible with this device, but this known device is fundamentally unsuited for analyzing flue gas in a solid fuel furnace.
In a measuring method mentioned in DE 10 2007 041 369 A1 in order to determine the amount of dust in the flue gas of a solid fuel furnace, a predefined amount of the flue gas flews through a vibratory tube, whereupon a quantity of dust deposits on a filter device of the tube. The tube is set in oscillation and the dust quantity is calculated from the deviation from the predetermined resonant frequency and/or natural frequency of the tube by an evaluating device.
Apart from the weighing device, the hose connections between a measuring probe to be introduced into the flue gas flow and the actual measuring device are of considerable importance. A measuring device with a weighing device comparable to DE 2 553 638 C2 is known from U.S. Pat. No. 7,947,503 B2. In this measuring device, a heated suction hose is provided between a gas inlet opening and the weighing device. By heating the suction hose, particles are prevented from depositing in the hose upstream of the weighing device and distorting the measurement results. Measuring accuracy is appreciably increased through this step.
However, the measuring device known from U.S. Pat. No. 7,947,503 B2 is not suitable for measuring fine particulates compliant to 1st BImSchV.